1. Field of the Invention
This invention relates to an electrode structure for a semiconductor device, having a semiconductor device consisting of silicon formed on a substrate to detect any physical quantity of the substrate and to convert it into an electrical signal; and an electrode wiring formed on the semiconductor device to transfer the electric signal to the outside, and also to a method for producing the same, which is allowed to be used for example as a pressure sensor chip for pressure detection of a high-temperature vapor, pressure detection in a combustion engine system, detection of molding pressure in resin injection, and so on.
2. Background of the Invention
Conventionally, a sensor chip, which has a semiconductor device formed on a small silicon substrate or the like and converting a physical quantity of the substrate into an electrical signal, and electrode wiring formed on the semiconductor device and transferring the electrical signal to the outside, is used as a sensor used for a built-in control and so on. The small sensor as described above does not need a large space for attachment, so that multiple measuring points are located in case of necessity, resulting in a control system with the high-precision. For example, there is the pressure sensor for the existing built-in control shown in FIG. 8, which has a built-in pressure sensor chip therein.
A pressure sensor 1 is composed of a main body 2, a fluid introduction 3 connected to one end of the main body 2, and a lead wire accommodation 4 connected to the other end of the main body 2.
A pressure-sensor module 11 is accommodated in the main body 2. A fluid introducing port 5 is formed in the fluid introduction 3 to guide fluid which its pressure is measured. A lead wire 6, transferring an electric signal to a signal processing means provided at the outside (not shown in FIG. 8), is accommodated and secured in the lead wire accommodation 4.
The pressure-sensor module 11 is, in turn, composed of a pressure-sensor chip 21 detecting the pressure of the fluid and converting it into the electric signal, a support 12 supporting the pressure-sensor chip 21, a case 13 covering the pressure-sensor chip 21 to be adhered to the support 12, and a pedestal 14 provided between the pressure-sensor chip 21 and the support 12.
The support 12 has a hole 15 which connects the fluid introducing port 5 from the bottom of the hole 15 to a through-hole 16, formed in the pedestal 14, from the top of the hole 15. The fluid to be measured is guided through the fluid introducing port 5, the hole 5 of the support 12 and the through-hole 16 of the pedestal 14 to the pressure-sensor chip 21.
A repeating base 17 is provided to the case 13 to go through the inside to the outside of the case 13. An inner wiring 18 links the repeating base 17 to the pressure-sensor chip 21. And further, an I/O terminal 19 for connecting to the lead wire 6 is provided on the outside of the repeating base 17.
As shown in FIG. 9, the pressure-sensor chip 21 is, in turn, composed of a diaphragm 31 secured on the pedestal 14, a semiconductor device 41 and an electrode wiring 51, which are formed on the diaphragm 31.
The diaphragm 31 has a leg 32 jointed to the pedestal 14, and a substrate 33, which deforms in response to the pressure change of the measured fluid, to work as a pressure sensing device. The semiconductor device 41 is formed on the substrate 33 on an insulation film 34. A protective film 35, having an opening for connecting to the electrode wiring 51, covers the upper face of the semiconductor device 41. The electrode wiring 51 is formed on the protective film 35 to connect through the opening, formed on the protective film 35, to the semiconductor device 41.
As shown in a schematic view of FIG. 10, the four semiconductor devices 41 are formed on the substrate 33, which are mutually linked by means of the electrode wiring 51, thereby forming a bridged circuit 52 in which the four semiconductor devices 41 compose a distortion meter. And the inner wiring 18 is connected to an I/O terminal 53 provided at the end of the bridged circuit 52.
The aforementioned deformation of the substrate 33 is converted into the electric signal by the semiconductor device 41. The converted electric signal is transferred through the electrode wiring 51, the inner wiring 18, the repeating base 17, the I/O terminal 19 and the lead wire 6 to signal processing means placed outside.
The pressure-sensor 1 having the aforementioned structured can be used for detecting the pressure of the high-temperature vapor, the pressure in a combustion engine system, or the molding pressure of the resin injection. Under the high-temperature condition in the aforementioned cases, an SOI (Silicon On Insulator) type pressure-sensor chip, such as the aforementioned pressure-sensor chip 21 in which the insulation film 34 is formed between the substrate 33 and the semiconductor device 41, is used.
As shown in a fragmentary enlarged sectional view of FIG. 11, in an electrode structure 71 for the semiconductor device of the conventional SOI type pressure-sensor chip 21, a contact area 42 is formed by incorporating boron in a part of the silicon semiconductor device 41. The aluminium-made electrode wiring 51 is connected to the contact area 42.
In the pressure-sensor chip 21 having the above structure, when the temperature of the atmosphere of the pressure sensor 1 is raised up to the high-temperature atmosphere of more than 300.degree. C., the aluminium of the electrode wiring 51 diffuses by reacting with the silicon of the semiconductor device 41, so that the resistance of the semiconductor device 41 is partially changed, thus making it difficult to obtain an accurate distortion resistance value under the high-temperature condition.
For this reason, as shown in FIG. 12, Japanese Patent Application Laid-open No. Hei4-350973 discloses an electrode structure 171 for the semiconductor device in which a barrier layer 61, formed of high-melting nitriding metal (titanium nitride), and a high-melting metal (titanium) layer 62 are provided between the contact area 42 and the electrode wiring 151 formed by using any one of gold (Au), platinum (Pt), and nickel (Ni).
According to the above electrode structure 171 for the semiconductor device, metal which forms the electrode wiring 151 does not diffuse into silicon of the semiconductor device 41 because of the barrier layer 61, so that the distortion resistance value of the semiconductor device 41 does not change under the high-temperature condition. Incidentally, the titanium layer 62 as the high-melting metal layer is provided in order to ensure an ohmic contact with the contact area 42.
However, in the electrode structure 171 for the semiconductor device, the electrode wiring 151 and the barrier layer 61 are bonded, but the touched faces may be peeled from each other because of the weak bonding force of the high-melting metal nitride (titanium nitride) and Au, Pt or Ni, thus making it difficult for the sensor chip to get stable performance for detecting a physical quantity such as distortion.
The object of the present invention is to provide an electrode structure for a semiconductor device and a method for producing the same, in which it is allowed that electrode wiring does not diffuse into silicon of the semiconductor device and a bonding force between a contact area of the semiconductor device and the electrode wiring is secure.